It contains 2 internal sides, one which blocks all incoming and outgoing signal transmissions to your cell phone. Additionally, smart keys, credit cards, passports, other RF enabled electronic devices, and anything that is RFID chipped, will be protected inside the RF shielding lining. The second side, blocks RFID / NFC only.
Additional Info: Wireless signal / RFID / NFC
Radio-frequency identification (RFID) is the use of a wireless data transmissions attached to an object, such as your credit card or passport. This information can be lifted, skimmed or scanned by anyone with simple technology.
Near Field Communication (NFC) is just like RFID except it can communicate both ways making data transferable to and from a chip. This is what Google Wallet and Apple Pay utilize for transmission of your credit card information at a point of purchase.
Wireless signals (radio frequency or RF) are used in communication for your phone, tablet, car radio, computer, credit card, etc. The electronic transmission of this data is done wirelessly and poses many problems to your security and privacy. It makes all of your information open to be intercepted.